Mechanical projectors broadly comprise devices having one or more movable launching members, which are moved as by pulling of a drawstring from a rest position to an advanced firing position against the resistance of one or more elastic elements, so that upon release, a projectile is rapidly accelerated so as to be launched by the return motion of the launching member. Such projectors include archery bows, cross bows, slingshots, and spring guns. In an archery bow, the limbs of the bow comprise the elastic elements resisting the drawing of the drawstring, while in a sling shots, this element is usually comprised of a stretchable strip, itself also comprising the launching element.
In most of these devices, except for the mechanically triggered crossbows, the exertion required by the user typically is at a maximum in the fully drawn aiming position, so that accuracy is adversely affected and for high powered devices, it is difficult to hold the drawstring in the firing position for any length of time.
There has thus heretofore been developed variable leverage devices particularly for archery bows in which the drawstring acts to bend the limbs through eccentric reels so that as the drawstring reaches the full draw position, the effort required falls off to make aiming steadier as a result of the greatly reduced effort required to hold a full draw. See U.S. Pat. No. 3,486,495 to Allen for an example as such an arrangement. Such bows have thus met with great success.
An advantage of the "Allen" bows is that the wind up and pay out of the drawstring on and off the reels allows the use of shorter and stiffer bow members, since the extension of the drawstring necessary to allow a full draw is made up only partly by the bending of the limb tips, the remainder by pay out of the reels. The drawstring payout is limited in the eccentric reel Allen bows by the diameter of these reels, and to greatly shorten the bow member would require excessively large reels.
It would be desirable to apply such variable leverage effect to other mechanical projectors, such as sling shots, but the absence of yielding limbs in a slingshot this would require overly large reels to establish sufficient drawstring payout to accommodate the drawing motion.
Accordingly, it is an object of the present invention to provide a variable leverage arrangement for mechanical projector in which the drawing motion is achieved substantially entirely from the payout of drawstring from the variable leverage device.
It is another object of the present invention to provide a variable leverage device for a sling shot type mechanical projector in which the launching element may be relatively unyielding, and in which separate elastic elements are incorporated to provide the projectile accelerating forces.